Section II. REPAIR OF COOLING SYSTEM

press on drive mechanism (20). Apply thin coating of

(7) Replace end frame and position drive end

grease before pressing on drive assembly.

housing on field frame. Make certain both commutator

end frame and drive housing are correctly positioned on

NOTE

field frame dowels (27). Then insert the through bolts

If drive mechanism is rotated to full

(15) and tighten securely.

extended lock position on crew shaft

during

replacement

during

3-4. Ignition Coil

overhaul of cranking motor, do not

attempt to force it in the reverse

Test the coil for grounded or open circuits by using a test

direction. Proceed to install drive

lamp as follows:

even though it is fully extended.

a. Primary Circuit Continuity Test.

After starter motor is installed on

(1) Check the primary circuit by placing the

engine and the engine starts.

test probes of a test light on the two primary terminals.

centrifugal force will demesh drive

(2) If the lamp does not light the primary

pinion from flywheel ring gear in the

circuit is open and the coil must be replaced.

usual manner.

b. Secondary Circuit Continuity Test.

(5) Place drive end housing (26) on armature

(1) Check the secondary circuit by placing

shaft after placing a few drops of oil on bushing (24).

one test probe of a test light on the high tension terminal

Then fasten center bearing (25) on drive housing (26).

and the other test probe on one of the primary terminals.

(6) Place spacer (17) on commutator end of

(2) The lamp will not light but sparks will be

armature shaft and install armature (18) complete with

noted as the test probe is rubbed over the terminal.

drive housing (26) in field frame assembly.

If no sparks occur, the secondary circuit is open and the

While installing armature, pull commutator end frame

coil must be replaced.

away from field frame and make certain brushes are

seated correctly on commutator.

Section II. REPAIR OF COOLING SYSTEM

cooling fan to provide positive full airflow through radiator

3-5. Description

core, a fan shroud is provided. An overflow tube

The cooling system carries off excess heat from the

connected to filler neck leads to bottom of radiator.

engine and holds engine at an efficient operating

Radiator incorporates a transmission oil cooler in bottom

temperature. System includes radiator, water pump,

tank. A double acting valve is provided in radiator cap

engine temperature gauge and sending unit, thermostat,

for relieving pressure due to expansion (from heating of

cooling fan, and coolant passages in the cylinder block

coolant) and allows atmospheric pressure to enter when

and cylinder head. Centrifugal water pump, which is

contraction (due to cooling of coolant) occurs.

driven by "V" belt from crankshaft pulley, draws coolant

b. Removal and Installation. Refer to TM 103930-

from bottom of radiator to top of cylinder block, from

618-20.

where there is forced circulation of coolant through

c. Cleaning and Inspection. Refer to TM 1039 30-

cylinder block and cylinder head. Coolant is discharged

618-20.

from cylinder head into coolant outlet manifold and

d. Repair.

passes through thermostat and tubing to upper tank of

(1) Radiator core. Use standard operating

radiator. Heat is removed from coolant as it passes from

procedures for repair of radiator core.

top to bottom of radiator by air forced through radiator

(2) Heat exchangers.

core by pusher type cooling fan.

(a) Sweat heat exchanger loose from bottom of

Engine has a pressure type cooling system which

permits higher coolant operating temperatures. It is

radiator core.

(b) Plug one port of heat exchanger, then apply

necessary to keep radiator cap turned on tightly at all

times to prevent loss of pressure. A thermostat, located

controlled air pressure to remaining port.

in the thermostat housing operates automatically to

NOTE

maintain a minimum coolant operating temperature of

Place heat exchanger under water as

1650F. This section covers direct and general support

air pressure is applied to expedite

maintenance procedures authorized by the Maintenance

leak location.

Allocation Chart.

3-6. Radiator

surface of heat exchanger.

a. Description.

Fin and tube type radiator is

(d) Prepare surface of heat exchanger to

supported in truck frame and protected from damage by

a heavy grille mounted in the counterweight. In order for

3-7